取代铁卟啉催化氧化邻硝基甲苯绿色合成邻硝基苯甲酸

Novel green synthesis of o-nitrobenzoic acid by oxidation of o-nitrotoluene with substituted iron porphyrins

研究了一种在乙醇水溶液中,以取代铁卟啉为仿生催化剂,催化氧气氧化邻硝基甲苯绿色合成邻硝基苯甲酸的新方法。考察了不同取代铁卟啉催化剂对反应活性和主产物选择性的影响,发现所有铁卟啉均有活性,且卟啉环外取代基从强给电子基(—OH)到吸电子基(—NO2)变化时,其催化活性(原料转化率)变化不大,但对主产物的选择性影响却很明显,其中T(p-Cl)PPFeCl的催化活性和选择性均为最好,含最强给电子基(—OH)或最强吸电子基(—NO2)的金属卟啉对主产物的选择性均最低。考察了溶剂中乙醇的体积分数对反应的影响,发现在乙醇浓度为80%时,产物的选择性最高。系统地考察了碱浓度、氧气压力、温度、时间、原料初始浓度等因素对反应的影响,找到了优化的工艺条件。发现以T(p-Cl)PPFeCl为催化剂,当乙醇浓度为80%、碱浓度为3.75mol.L-1时,在2.0MPa、55℃条件下反应12h,邻硝基甲苯的转化率达到79.7%,邻硝基苯甲酸的选择性和收率分别可达95.8%和76.3%。

A novel green synthesis of o-nitrobenzoic acid by aerobic oxidation of o-nitrotoluene with aqueous ethanol instead of pure methanol as the solvent and substituted iron porphyrins as biomimetic catalysts was investigated.The effects of six iron porphyrins with different peripheral substituents on the above reaction were studied.It was found that all iron porphyrins had catalytic activity,and the substituents from strong electron donating group（—OH）to electron withdrawing group（—NO2）had a remarkable effect on the selectivity of o-nitrobenzoic acid and a insignificant effect on the activity（conversion of o-nitrotoluene）.Among the six iron porphyrins T（p-Cl）PPFeCl had the highest catalytic activity and selectivity at the same time.By introducing a stronger electron withdrawing substituent,such as —NO2 or strong electron donating group,such as —OH around the porphyrin rings resulted in low catalytic activity and selectivity.Moreover,the effects of different process parameters,such as ethanol concentration,NaOH concentration,dioxygen pressure,temperature,reaction time and initial concentration of o-nitrotoluene on the above reaction were examined,and optimal conditions were obtained.The conversion of o-nitrotoluene,the selectivity and yield of product could reach 79.7%,95.8% and 76.3% respectively by using aqueous ethanol of 80% instead of pure methanol as solvent and T（p-Cl）PPFeCl as catalyst,and the reaction was carried out under optimal conditions,such as NaOH concentration of 3.75 mol·L^-1,2.0 MPa O2 at 55℃ for 12 h.